Add tracing option (#487)

Adds a middleware to enable tracing with OpenTracing/OpenZipkin.
Enabling tracing will have a large impact on performance so it is
not advisable in production.

middleware/trace/setup_test.go

@@ -0,0 +1,43 @@
+package trace
+
+import (
+	"testing"
+
+	"github.com/mholt/caddy"
+)
+
+func TestTraceParse(t *testing.T) {
+	tests := []struct {
+		input     string
+		shouldErr bool
+		endpoint      string
+	}{
+		// oks
+		{`trace`, false, "http://localhost:9411/api/v1/spans"},
+		{`trace localhost:1234`, false, "http://localhost:1234/api/v1/spans"},
+		{`trace http://localhost:1234/somewhere/else`, false, "http://localhost:1234/somewhere/else"},
+		{`trace zipkin localhost:1234`, false, "http://localhost:1234/api/v1/spans"},
+		{`trace zipkin http://localhost:1234/somewhere/else`, false, "http://localhost:1234/somewhere/else"},
+		// fails
+		{`trace footype localhost:4321`, true, ""},
+	}
+	for i, test := range tests {
+		c := caddy.NewTestController("dns", test.input)
+		m, err := traceParse(c)
+		if test.shouldErr && err == nil {
+			t.Errorf("Test %v: Expected error but found nil", i)
+			continue
+		} else if !test.shouldErr && err != nil {
+			t.Errorf("Test %v: Expected no error but found error: %v", i, err)
+			continue
+		}
+
+		if test.shouldErr {
+			continue
+		}
+
+		if test.endpoint != m.Endpoint {
+			t.Errorf("Test %v: Expected endpoint %s but found: %s", i, test.endpoint, m.Endpoint)
+		}
+	}
+}